libstdc++
span
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1// Components for manipulating non-owning sequences of objects -*- C++ -*-
2
3// Copyright (C) 2019-2023 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file span
26 * This is a Standard C++ Library header.
27 */
28
29//
30// P0122 span library
31// Contributed by ThePhD
32//
33
34#ifndef _GLIBCXX_SPAN
35#define _GLIBCXX_SPAN 1
36
37#pragma GCC system_header
38
39#if __cplusplus > 201703L
40
41#include <array>
42#include <cstddef>
43#include <bits/stl_iterator.h>
44#include <bits/ranges_base.h>
45
46#if __cpp_lib_concepts
47namespace std _GLIBCXX_VISIBILITY(default)
48{
49_GLIBCXX_BEGIN_NAMESPACE_VERSION
50
51#define __cpp_lib_span 202002L
52
53 inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
54
55 template<typename _Type, size_t _Extent>
56 class span;
57
58 namespace __detail
59 {
60 template<typename _Tp>
61 inline constexpr bool __is_span = false;
62
63 template<typename _Tp, size_t _Num>
64 inline constexpr bool __is_span<span<_Tp, _Num>> = true;
65
66 template<typename _Tp>
67 inline constexpr bool __is_std_array = false;
68
69 template<typename _Tp, size_t _Num>
70 inline constexpr bool __is_std_array<std::array<_Tp, _Num>> = true;
71
72 template<size_t _Extent>
73 class __extent_storage
74 {
75 public:
76 constexpr
77 __extent_storage(size_t) noexcept
78 { }
79
80 static constexpr size_t
81 _M_extent() noexcept
82 { return _Extent; }
83 };
84
85 template<>
86 class __extent_storage<dynamic_extent>
87 {
88 public:
89 constexpr
90 __extent_storage(size_t __extent) noexcept
91 : _M_extent_value(__extent)
92 { }
93
94 constexpr size_t
95 _M_extent() const noexcept
96 { return this->_M_extent_value; }
97
98 private:
99 size_t _M_extent_value;
100 };
101 } // namespace __detail
102
103 template<typename _Type, size_t _Extent = dynamic_extent>
104 class span
105 {
106 template<size_t _Offset, size_t _Count>
107 static constexpr size_t
108 _S_subspan_extent()
109 {
110 if constexpr (_Count != dynamic_extent)
111 return _Count;
112 else if constexpr (extent != dynamic_extent)
113 return _Extent - _Offset;
114 else
115 return dynamic_extent;
116 }
117
118 // _GLIBCXX_RESOLVE_LIB_DEFECTS
119 // 3255. span's array constructor is too strict
120 template<typename _Tp, size_t _ArrayExtent>
121 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
122 using __is_compatible_array = __is_array_convertible<_Type, _Tp>;
123
124 template<typename _Ref>
125 using __is_compatible_ref
126 = __is_array_convertible<_Type, remove_reference_t<_Ref>>;
127
128 public:
129 // member types
130 using element_type = _Type;
131 using value_type = remove_cv_t<_Type>;
132 using size_type = size_t;
133 using difference_type = ptrdiff_t;
134 using pointer = _Type*;
135 using const_pointer = const _Type*;
136 using reference = element_type&;
137 using const_reference = const element_type&;
138 using iterator = __gnu_cxx::__normal_iterator<pointer, span>;
139 using reverse_iterator = std::reverse_iterator<iterator>;
140#if __cplusplus > 202002L
141 using const_iterator = std::const_iterator<iterator>;
142 using const_reverse_iterator = std::const_iterator<reverse_iterator>;
143#endif
144
145 // member constants
146 static constexpr size_t extent = _Extent;
147
148 // constructors, copy and assignment
149
150 constexpr
151 span() noexcept
152 requires (_Extent == dynamic_extent || _Extent == 0)
153 : _M_ptr(nullptr), _M_extent(0)
154 { }
155
156 template<contiguous_iterator _It>
157 requires __is_compatible_ref<iter_reference_t<_It>>::value
158 constexpr explicit(extent != dynamic_extent)
159 span(_It __first, size_type __count)
160 noexcept
161 : _M_ptr(std::to_address(__first)), _M_extent(__count)
162 {
163 if constexpr (_Extent != dynamic_extent)
164 {
165 __glibcxx_assert(__count == _Extent);
166 }
167 __glibcxx_requires_valid_range(__first, __first + __count);
168 }
169
170 template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
171 requires __is_compatible_ref<iter_reference_t<_It>>::value
172 && (!is_convertible_v<_End, size_type>)
173 constexpr explicit(extent != dynamic_extent)
174 span(_It __first, _End __last)
175 noexcept(noexcept(__last - __first))
176 : _M_ptr(std::to_address(__first)),
177 _M_extent(static_cast<size_type>(__last - __first))
178 {
179 if constexpr (_Extent != dynamic_extent)
180 {
181 __glibcxx_assert((__last - __first) == _Extent);
182 }
183 __glibcxx_requires_valid_range(__first, __last);
184 }
185
186 template<size_t _ArrayExtent>
187 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
188 constexpr
189 span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
190 : span(static_cast<pointer>(__arr), _ArrayExtent)
191 { }
192
193 template<typename _Tp, size_t _ArrayExtent>
194 requires __is_compatible_array<_Tp, _ArrayExtent>::value
195 constexpr
196 span(array<_Tp, _ArrayExtent>& __arr) noexcept
197 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
198 { }
199
200 template<typename _Tp, size_t _ArrayExtent>
201 requires __is_compatible_array<const _Tp, _ArrayExtent>::value
202 constexpr
203 span(const array<_Tp, _ArrayExtent>& __arr) noexcept
204 : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
205 { }
206
207 template<typename _Range>
208 requires (!__detail::__is_span<remove_cvref_t<_Range>>)
209 && (!__detail::__is_std_array<remove_cvref_t<_Range>>)
210 && (!is_array_v<remove_cvref_t<_Range>>)
211 && ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
212 && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
213 && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
214 constexpr explicit(extent != dynamic_extent)
215 span(_Range&& __range)
216 noexcept(noexcept(ranges::data(__range))
217 && noexcept(ranges::size(__range)))
218 : span(ranges::data(__range), ranges::size(__range))
219 {
220 if constexpr (extent != dynamic_extent)
221 {
222 __glibcxx_assert(ranges::size(__range) == extent);
223 }
224 }
225
226 constexpr
227 span(const span&) noexcept = default;
228
229 template<typename _OType, size_t _OExtent>
230 requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
231 || _Extent == _OExtent)
232 && (__is_array_convertible<_Type, _OType>::value)
233 constexpr
234 explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
235 span(const span<_OType, _OExtent>& __s) noexcept
236 : _M_extent(__s.size()), _M_ptr(__s.data())
237 {
238 if constexpr (extent != dynamic_extent)
239 {
240 __glibcxx_assert(__s.size() == extent);
241 }
242 }
243
244 ~span() noexcept = default;
245
246 constexpr span&
247 operator=(const span&) noexcept = default;
248
249 // observers
250
251 [[nodiscard]]
252 constexpr size_type
253 size() const noexcept
254 { return this->_M_extent._M_extent(); }
255
256 [[nodiscard]]
257 constexpr size_type
258 size_bytes() const noexcept
259 { return this->_M_extent._M_extent() * sizeof(element_type); }
260
261 [[nodiscard]]
262 constexpr bool
263 empty() const noexcept
264 { return size() == 0; }
265
266 // element access
267
268 [[nodiscard]]
269 constexpr reference
270 front() const noexcept
271 {
272 __glibcxx_assert(!empty());
273 return *this->_M_ptr;
274 }
275
276 [[nodiscard]]
277 constexpr reference
278 back() const noexcept
279 {
280 __glibcxx_assert(!empty());
281 return *(this->_M_ptr + (size() - 1));
282 }
283
284 [[nodiscard]]
285 constexpr reference
286 operator[](size_type __idx) const noexcept
287 {
288 __glibcxx_assert(__idx < size());
289 return *(this->_M_ptr + __idx);
290 }
291
292 [[nodiscard]]
293 constexpr pointer
294 data() const noexcept
295 { return this->_M_ptr; }
296
297 // iterator support
298
299 [[nodiscard]]
300 constexpr iterator
301 begin() const noexcept
302 { return iterator(this->_M_ptr); }
303
304 [[nodiscard]]
305 constexpr iterator
306 end() const noexcept
307 { return iterator(this->_M_ptr + this->size()); }
308
309 [[nodiscard]]
310 constexpr reverse_iterator
311 rbegin() const noexcept
312 { return reverse_iterator(this->end()); }
313
314 [[nodiscard]]
315 constexpr reverse_iterator
316 rend() const noexcept
317 { return reverse_iterator(this->begin()); }
318
319#if __cplusplus > 202002L
320 [[nodiscard]]
321 constexpr const_iterator
322 cbegin() const noexcept
323 { return begin(); }
324
325 [[nodiscard]]
326 constexpr const_iterator
327 cend() const noexcept
328 { return end(); }
329
330 [[nodiscard]]
331 constexpr const_reverse_iterator
332 crbegin() const noexcept
333 { return rbegin(); }
334
335 [[nodiscard]]
336 constexpr const_reverse_iterator
337 crend() const noexcept
338 { return rend(); }
339#endif
340
341 // subviews
342
343 template<size_t _Count>
344 [[nodiscard]]
345 constexpr span<element_type, _Count>
346 first() const noexcept
347 {
348 if constexpr (_Extent == dynamic_extent)
349 __glibcxx_assert(_Count <= size());
350 else
351 static_assert(_Count <= extent);
352 using _Sp = span<element_type, _Count>;
353 return _Sp{ this->data(), _Count };
354 }
355
356 [[nodiscard]]
357 constexpr span<element_type, dynamic_extent>
358 first(size_type __count) const noexcept
359 {
360 __glibcxx_assert(__count <= size());
361 return { this->data(), __count };
362 }
363
364 template<size_t _Count>
365 [[nodiscard]]
366 constexpr span<element_type, _Count>
367 last() const noexcept
368 {
369 if constexpr (_Extent == dynamic_extent)
370 __glibcxx_assert(_Count <= size());
371 else
372 static_assert(_Count <= extent);
373 using _Sp = span<element_type, _Count>;
374 return _Sp{ this->data() + (this->size() - _Count), _Count };
375 }
376
377 [[nodiscard]]
378 constexpr span<element_type, dynamic_extent>
379 last(size_type __count) const noexcept
380 {
381 __glibcxx_assert(__count <= size());
382 return { this->data() + (this->size() - __count), __count };
383 }
384
385 template<size_t _Offset, size_t _Count = dynamic_extent>
386 [[nodiscard]]
387 constexpr auto
388 subspan() const noexcept
389 -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
390 {
391 if constexpr (_Extent == dynamic_extent)
392 {
393 __glibcxx_assert(_Offset <= size());
394 }
395 else
396 static_assert(_Offset <= extent);
397
398 using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
399
400 if constexpr (_Count == dynamic_extent)
401 return _Sp{ this->data() + _Offset, this->size() - _Offset };
402 else
403 {
404 if constexpr (_Extent == dynamic_extent)
405 {
406 __glibcxx_assert(_Count <= size());
407 __glibcxx_assert(_Count <= (size() - _Offset));
408 }
409 else
410 {
411 static_assert(_Count <= extent);
412 static_assert(_Count <= (extent - _Offset));
413 }
414 return _Sp{ this->data() + _Offset, _Count };
415 }
416 }
417
418 [[nodiscard]]
419 constexpr span<element_type, dynamic_extent>
420 subspan(size_type __offset, size_type __count = dynamic_extent) const
421 noexcept
422 {
423 __glibcxx_assert(__offset <= size());
424 if (__count == dynamic_extent)
425 __count = this->size() - __offset;
426 else
427 {
428 __glibcxx_assert(__count <= size());
429 __glibcxx_assert(__offset + __count <= size());
430 }
431 return {this->data() + __offset, __count};
432 }
433
434 private:
435 pointer _M_ptr;
436 [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
437 };
438
439 // deduction guides
440
441 template<typename _Type, size_t _ArrayExtent>
442 span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
443
444 template<typename _Type, size_t _ArrayExtent>
445 span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
446
447 template<typename _Type, size_t _ArrayExtent>
448 span(const array<_Type, _ArrayExtent>&)
449 -> span<const _Type, _ArrayExtent>;
450
451 template<contiguous_iterator _Iter, typename _End>
452 span(_Iter, _End)
453 -> span<remove_reference_t<iter_reference_t<_Iter>>>;
454
455 template<ranges::contiguous_range _Range>
456 span(_Range &&)
457 -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
458
459 template<typename _Type, size_t _Extent>
460 [[nodiscard]]
461 inline
462 span<const byte, _Extent == dynamic_extent
463 ? dynamic_extent : _Extent * sizeof(_Type)>
464 as_bytes(span<_Type, _Extent> __sp) noexcept
465 {
466 auto data = reinterpret_cast<const byte*>(__sp.data());
467 auto size = __sp.size_bytes();
468 constexpr auto extent = _Extent == dynamic_extent
469 ? dynamic_extent : _Extent * sizeof(_Type);
470 return span<const byte, extent>{data, size};
471 }
472
473 template<typename _Type, size_t _Extent>
474 requires (!is_const_v<_Type>)
475 inline
476 span<byte, _Extent == dynamic_extent
477 ? dynamic_extent : _Extent * sizeof(_Type)>
478 as_writable_bytes [[nodiscard]] (span<_Type, _Extent> __sp) noexcept
479 {
480 auto data = reinterpret_cast<byte*>(__sp.data());
481 auto size = __sp.size_bytes();
482 constexpr auto extent = _Extent == dynamic_extent
483 ? dynamic_extent : _Extent * sizeof(_Type);
484 return span<byte, extent>{data, size};
485 }
486
487 namespace ranges
488 {
489 // Opt-in to borrowed_range concept
490 template<typename _ElementType, size_t _Extent>
491 inline constexpr bool
492 enable_borrowed_range<span<_ElementType, _Extent>> = true;
493
494 // Opt-in to view concept
495 template<typename _ElementType, size_t _Extent>
496 inline constexpr bool
497 enable_view<span<_ElementType, _Extent>> = true;
498 }
499_GLIBCXX_END_NAMESPACE_VERSION
500} // namespace std
501#endif // concepts
502#endif // C++20
503#endif // _GLIBCXX_SPAN